A CT scan is a common imaging test, but how you prepare in the hours before it can affect the results. The most common mistakes involve eating when you shouldn’t, wearing the wrong clothing, and forgetting to tell your doctor about medications or allergies. The single most important rule is to follow the specific instructions your imaging center gives you, because preparation differs depending on the type of scan and whether contrast dye is used.
What Not To Do Before A CT Scan Prep Mistakes
The biggest mistake patients make is assuming every CT scan has the same prep. A CT scan of your head does not require the same preparation as a CT scan of your abdomen or pelvis. Your doctor orders a specific test, and the instructions are tailored to that test. Ignoring these instructions is the root cause of most canceled or repeated scans.
If you are having an abdominal or pelvic scan, you may be told to stop eating and drinking for several hours beforehand. This is not a suggestion. Food in your stomach or intestines can block the view of the organs the radiologist needs to see. When the images are unclear, you may be asked to reschedule and start over.
Another common error is not telling your provider about all medications you take. Some medications, particularly those for diabetes, interact with the contrast dye used in CT scans. You may need to adjust your dose on the day of the scan. Never stop a medication on your own. Always ask the ordering physician or the imaging center what to do.
Can I Eat or Drink Before My CT Scan?
It depends entirely on the area being scanned. For most CT scans of the head, chest, or bones, you can typically eat and drink normally before the test. For CT scans of the abdomen and pelvis, fasting is usually required.
If your doctor tells you to fast, that usually means no solid food for 4 to 6 hours before the scan. Clear liquids, such as water, black coffee, or clear broth, are often allowed. However, you should avoid dairy products and anything that contains fat, as these slow digestion. Chewing gum and hard candies can also stimulate your stomach and should be avoided during a fast.
If you are unsure whether you can eat, call the imaging center. Guessing is a mistake. Showing up having eaten when you were supposed to fast means your scan may be delayed or canceled.
What Should I Wear and What Should I Remove?
Wear comfortable clothing without metal. Metal interferes with the CT scanner’s X-ray beam and creates artifacts on the images. These artifacts can obscure the area being examined and may require a repeat scan.
Avoid clothing with zippers, snaps, buttons, or underwire bras. You will likely be asked to change into a hospital gown if your clothing has any metal. Save time by wearing simple items like sweatpants, a t-shirt, or a loose-fitting top.
You must also remove all jewelry, including earrings, necklaces, rings, and piercings. Watches, glasses, and hairpins also need to come off. Dentures and hearing aids may need to be removed depending on the area being scanned. The technologist will give you a secure place to store your belongings.
What About Contrast Dye and Allergies?
Many CT scans use contrast dye, also called contrast material, to make certain tissues and blood vessels show up more clearly. This dye is often given through an IV, but it can also be swallowed. If your scan requires contrast, you need to know about any allergies you have.
Some people have allergic reactions to the contrast material. Reactions range from mild, such as nausea or itching, to severe, including difficulty breathing. It is critical to tell your doctor and the imaging technologist about any allergies you have, especially if you have had a reaction to contrast dye in the past.
If you have a history of reaction to contrast, your doctor may prescribe medications to take before the scan to reduce the risk. Do not skip these medications. Also, tell your provider if you have kidney disease or diabetes. The contrast dye is cleared by the kidneys, and your doctor may need to check your kidney function before the scan.
One specific mistake is failing to mention that you take metformin, a common diabetes medication. Because metformin is processed by the kidneys, combining it with contrast dye can rarely cause a serious condition called lactic acidosis. Your doctor may tell you to hold your metformin dose on the day of the scan and for a period afterward. This decision is made based on your kidney function and the type of scan.
Do I Need to Stop Taking My Medications?
Do not stop any medication without explicit instructions from your doctor. Most medications can be taken as usual on the day of a CT scan. The exceptions relate primarily to diabetes medications, as mentioned, and sometimes to certain blood thinners if a biopsy is planned alongside the scan.
If you are having a CT-guided biopsy, which uses the CT scanner to guide a needle to a specific area, you may need to hold blood-thinning medications. This includes warfarin, apixaban, rivaroxaban, and others. Your doctor will give you specific instructions about when to stop and restart these medications. Do not make this decision on your own.
Always bring a current list of your medications to your appointment. This includes prescription drugs, over-the-counter medicines, and supplements. The technologist or nurse will review this list with you before the scan.
What If I Am Pregnant or Think I Might Be?
Tell your doctor and the technologist immediately if you are pregnant or think you could be pregnant. CT scans use ionizing radiation, and there is a small risk to a developing fetus. Doctors generally avoid CT scans during pregnancy unless the test is medically necessary and the benefit outweighs the risk.
If a scan is necessary, the technologist will take steps to minimize radiation exposure to the fetus. This is not a reason to panic, but it is a reason to be upfront. Do not withhold this information because you are embarrassed or worried about delaying the test. Your safety and the safety of your baby come first.
How Should I Prepare for a CT Scan with Oral Contrast?
Some abdominal and pelvic scans require you to drink a contrast solution before the scan. This is often called barium or Gastrografin. The timing of this drink is important. You will usually be told to drink a specific amount at a specific time before your appointment.
Do not drink the contrast earlier or later than instructed. If you drink it too early, it may have moved past the area of interest. If you drink it too late, it may not have reached the right part of your digestive tract. In either case, the scan may need to be repeated.
Oral contrast can cause nausea or constipation. These are common side effects and not usually a reason to skip the prep. If you vomit the contrast material shortly after drinking it, call the imaging center before your appointment. They may need to reschedule or change the plan.
Frequently Asked Questions
Can I drink coffee before a CT scan?
Black coffee is usually considered a clear liquid and may be allowed, but you must confirm with your imaging center. If you are fasting for an abdominal scan, do not add milk, cream, or sugar.
How long before a CT scan do I need to stop eating?
For scans that require fasting, you are typically asked to avoid solid food for 4 to 6 hours beforehand. Your specific instructions may differ, so follow what your doctor or imaging center tells you.
Can I take my blood pressure medication before a CT scan?
Yes, you should generally take your blood pressure medication as usual. Only diabetes medications and certain blood thinners may need to be adjusted, and only under your doctor’s direction.
What happens if I accidentally eat before my CT scan?
Tell the technologist when you arrive. They will determine if your scan can proceed or if it needs to be rescheduled, depending on the area being scanned and what you ate.
